1. Field of the Invention
The present invention relates generally to a power conversion apparatus using a heat pipe cooler.
2. Description of the Related Art
In a power conversion apparatus, generally, a semiconductor element is employed as a switching element. As a known method for cooling the semiconductor element, a heat pipe cooler is used. To cool the semiconductor element, the method uses an effect of thermal energy which moves from a high-temperature part to a low-temperature part through a refrigerant liquid (hereinafter, referred to as a refrigerant) enclosed in a heat pipe by the temperature difference between both ends of the heat pipe.
In a case where the heat pipe cooler is used in cold environment such as outdoors in cold regions, the refrigerant on the low-temperature side is frozen when the temperature on the low-temperature side in the heat pipe is less than or equal to the refrigerant freezing point. If the refrigerant is frozen, the transfer of thermal energy is severely disturbed. Thus, the heat pipe cooler cannot sufficiently exert its cooling effect. Therefore, when the power conversion apparatus is operated in a state where the refrigerant of the heat pipe cooler is frozen, the semiconductor element might be destroyed due to over-allowable temperature as the semiconductor element cannot be sufficiently cooled. To prevent the refrigerant of the heat pipe from freezing, various measures have been taken. For example, a power conversion apparatus in which a heater is attached to a heat pipe cooler is disclosed (For example, refer to Jpn. Pat. Appln. KOKAI Publication No. 6-276742).
However, the power conversion apparatus in which the heater is attached to the heat pipe cooler cannot be operated until the refrigerant is defrosted by the heater since the cooling performance of the heat pipe cooler is reduced during operation.